1. Field of the Invention
The present invention relates to a method for forming leadless semiconductor packages, and more particular, to a method for forming leadless semiconductor packages which is capable of reducing the number of saw blades used.
2. Description of the Prior Art
The conventional leadframe package has been applied widely for a long time in the integrated circuit package field. It has advantages such as low manufacturing cost, high reliability, and so forth. However, the conventional leadframe package possesses rather long outer leads and inner leads, and it is gradually unable to satisfy the development of the integrated circuits, which have high numbers of input/output (I/O) connections and tiny sizes. For this reason, a leadless semiconductor package is developed and applied gradually. Since it is leadless, it is capable of reducing the footprint and the package size. Moreover, since the length of the lead is shortened, the leadless semiconductor package has advantages of low electric resistance, inductance, and electric capacity, and it is very suitable for cell phones, personal digital assistants (PDAs), digital cameras, and so forth.
Please refer to FIG. 1 to FIG. 3. FIG. 1 to FIG. 3 are schematic diagrams of a method for forming a leadless semiconductor package 10 according to the prior art. As shown in FIG. 1, a unit 12 of a leadframe is provided at first. The unit 12 includes a die pad 14 and a plurality of leads 16. Therein, the unit 12 is composed of copper, iron, or an alloy of copper and iron, and a metal layer 18, which is composed of silver, is formed on an upper surface of the unit 12. A die 20 is adhered to the metal layer 18 of the die pad 14, and a plurality of conductive wires 21 are formed by wire bonding to electrically connect a plurality of bond pads (not shown in FIG. 1) on the die 20 with a plurality of bond regions 22, 24, 26, and 28 of the corresponding leads 16. Furthermore, an encapsulation 30 covers the unit 12 and exposes lower surfaces of the die pad 14 and the leads 16.
As shown in FIG. 2, a photoresist layer (not shown in FIG. 2) is formed on a lower surface of unit 12, and a photolithographic process is performed to form a patterned photoresist layer 32. Therein, the patterned photoresist layer 32 exposes the die pad 14 and the bond regions 22, 24, 26, and 28. Then, a metal layer 34, which is composed of tin or lead, is formed on the lower surfaces of the die pad 14 and the bond regions 22, 24, 26, and 28.
As shown in FIG. 3, the patterned photoresist layer 32 is removed. A cutting process is performed by utilizing a saw blade (not shown in FIG. 3) to remove a plurality of interval regions 36 of the leads 16 and cut off the metal layer 18 in the interval regions 36 to electrically isolate the bond regions 22, 24, 26, and 28. Finally, a leadless semiconductor package 10 is formed.
The method for forming the leadless semiconductor package 10 according to the prior art utilizes the saw blade to cut off the leads 16 and the metal layer 18 on the leads 16 directly. Since the material of the leads 16 is different from the material of the metal layer 18, it requires the expenditure of many saw blades and increases a lot of the manufacturing cost. For this reason, how to reduce the expenditure of saw blades is very important.